The neural crest is composed of multipotent precursor cells which invade all parts of the embryo and contribute to the development of a wide array of cell and tissues. Abnormalities of neural crest cells display a variety of phenotypes due to their diverse cellular potentials. The murine lethal spotting (ls) mutation serves as a model system to study factors involved in these processes, since Is/ls mice lack enteric ganglia in their terminal bowel and have white spots on their coat due to problems with melanocytes. This mouse also provides a genetic model for Hirschsprung's disease, a human disorder in which there is a lack of neural crest derived enteric ganglia in the distal colon. Identification and isolation of the gene responsible for the Is mutation is an important step towards understanding its role in neural crest cell migration, differentiation, survival, and/or function as well as for understanding its role in the disease process. We have established a high resolution molecular genetic linkage map of the Is region on mouse chromosome 2 using intersubspecific backcross analyses and determined the map position of Is mutation, we will chromosome walk to and physically clone the Is region. We will develop resources necessary to identify and characterize potential candidate genes from the smallest defined interval that must contain the Is gene. The combination of molecular and genetic approaches to be taken will provide the foundation for a comprehensive understanding of the Is gene and its functions. This research will provide an understanding of the complex cellular interactions occurring during development as well as an opportunity to investigate the potential role of the Is gene in neoplasia.